I decided to go out, even though it was only 46 degrees out with a clear and sunny sky. I replaced the syrup and decided against trying to remove the old unused quarter-patty. The combs were very deep and I would have to disturb the bees as a whole just to reach it.
I don't remember seeing an ant problem on the top of the bars when I opened the cover. Maybe the syrup near the hive has driven them away from the hive itself.